1. Field of the Invention
The invention relates to a spark-ignited internal combustion engine and a method of controlling the spark-ignited internal combustion engine.
2. Description of the Related Art
An available spark-ignited internal combustion engine includes a variable compression ratio mechanism that changes a mechanical compression ratio, and a variable valve timing mechanism that controls a valve closing timing at which an intake valve is closed, wherein during middle or high engine load operation, as a load applied to the engine decreases, the mechanical compression ratio is increased and the valve closing timing of the intake valve is retarded (see Japanese Patent Application Publication No. 2004-218522, for example).
When the mechanical compression ratio is increased, the volume of the combustion chamber decreases, and therefore, the space between the top surface of a piston and the inner surface of the cylinder head, the intake valve, and the exhaust valve when the piston reaches the top dead center is reduced. When this occurs, such a space is minimized when the mechanical compression ratio is brought to the maximum mechanical compression ratio. Meanwhile, the inertial force of the piston increases as the engine speed increases, and therefore, as the engine speed increases, the space between the top surface of the piston and the inner surface of the cylinder head, etc. is reduced because of elongation of a connecting rod that connects the piston and a crankshaft, for example.
Thus, when the engine speed increases while the mechanical compression ratio is high, there is a fear that the top surface of the piston interferes with the inner surface of the cylinder head, etc., and the probability of occurrence thereof becomes highest when the mechanical compression ratio is brought to the maximum mechanical compression ratio. However, in the above-described internal combustion engine, no consideration is given to such a fear.